1. Field of the Invention
This invention relates to new multifunctional organosilicon copolymers and their use as adhesion additives in curable organosiloxane compositions. Preferred compositions cure by a platinum group metal catalyzed hydrosilation reaction at temperatures of up to 100.degree. C.
2. Background Information
The curing characteristics of organosiloxane compositions and the properties of the cured materials obtained from these compositions are desirable for a variety of end use applications, particularly in the electrical and electronics areas. The cured materials are useful as protective coatings, potting materials and encapsulants for integrated circuits and other electronic devices and as coatings for printed circuit boards.
A shortcoming of organosiloxane compositions, particularly those that cure by a platinum group metal catalyzed hydrosilation reaction, is their inability to develop strong adhesion to many substrates, particularly plastics and certain metals. One method for remedying this deficiency is by using primer compositions or adhesion promoting additives containing one or more silanes and/or organosiloxanes with a plurality of silicon-bonded hydrolyzable groups and at least one organofunctional substituent that is bonded to silicon through at least one carbon atom.
Primer compositions are applied to substrates to which adhesion is desired prior to application of the curable organosiloxane composition. Adhesion promoters may also be present in the curable organosiloxane composition.
Adhesion promoting additives described in the prior art typically contain at least two functional groups.
U.S. Pat. Nos. 3,772,026 and 3,873,334 teach acyloxy functional silanes which additionally have silicon hydride or alkenyl functionality respectively. Although the acyloxy functionality is very reactive, it liberates corrosive acetic acid upon reaction with hydroxyl groups present at the surface of the substrate or with ambient moisture.
U.S. Pat. No. 4,196,273 teaches use of unsaturated alkoxysilanes, such as vinyltrimethoxysilane, as adhesion additives. Adhesion is not demonstrated at temperatures below 100.degree. C. and only adhesion to glass is demonstrated at 100.degree. C. U.S. Pat. No. 4,329,273 teaches use of partially hydrolyzed unsaturated alkoxysilanes. Curing of compositions containing these adhesion promoting additives did not occur at ambient laboratory temperatures, but cure at 100.degree. C. was demonstrated.
U.S. Pat. No. 4,082,726 teaches organosilicon compounds containing epoxy functional dialkoxysilyl groups and at least one alkenyl radical or hydrogen atom bonded to silicon in the organosilicon compound. Adhesion with compositions containing these compounds is demonstrated after cure at between 100.degree.-200.degree. C. U.S. Pat. No. 4,087,585 teaches physical blends of epoxy functional alkoxysilanes with silanol functional fluids containing alkenyl functionality. Cure was obtained at elevated temperatures. Multifunctional organosilanes containing ethylenic unsaturation, epoxy functionality, and alkoxy functionality are taught in U.S. Pat. No. 4,732,932. U.S. Pat. No. 5,106,933 teaches use of mixtures of alkoxysilanes.
U.S. Pat. Nos. 4,659,851, 4,719,262, and 4,906,686 teach reaction products of unsaturated alcohols with alkoxysilanes as adhesion promoting additives. The resultant Si-O-C bond between the unsaturated alcohol and alkoxysilane would be susceptible to hydrolysis such that the adhesion could be decreased upon exposure to moisture.
U.S. Pat. No. 4,077,943 teaches using an organohydrogensiloxane containing epoxy functionality as the curing agent for organosiloxane compositions. Japanese Laid Open Patent Application (JLOPA) 1/085,224 teaches accelerating the development of adhesion using organosiloxanes containing epoxy functional silsesquioxane units and optional ethylenic unsaturation, but no Si(OR).sub.3 functional groups. JLOPA 4/311,766 teaches adhesion promoting additives containing a) siloxane units with at least one alkoxysilylalkyl group, b) siloxane units with at least one terminally unsaturated alkenyl radical; c) trialkoxysiloxy units and d) SiO.sub.4/2 units. JLOPA 2/18452 describes adhesion promoters that include organosilicon compounds containing two silicon-bonded alkoxy groups and at least one epoxy group and organosilicon compounds containing at least one alkoxy group and at least two ethylenically unsaturated double bonds per molecule.
U.S. Pat. No 4,786,701 teaches adhesion promoters which are hydrolysis reaction products of tetraalkoxysilanes, alkenyl or silicon hydride functional organopolysiloxane, and optional (meth)acryloxy functional alkoxysilanes. U.S. Pat. No. 4,677,161 teaches silicon hydride functional SiO.sub.2 resins containing residual alkoxy groups, however no Si(OR).sub.3 groups are present.
None of the aforementioned patents demonstrate that adhesion can be achieved at temperatures below 100.degree. C. or to a variety of substrates.
One objective of this invention is to define a group of organosilicon compounds that impart adhesion between a) elastomers and other products prepared by curing organosiloxane compositions and b) a variety of organic and inorganic substrates that the compositions are in contact with during curing. Preferred additives impart adhesion at curing temperatures of up to 100.degree. C.